Earthing System – A Complete Technical Guide

(As per IEC, IEEE, SBC, and NEC standards)

1. Introduction

Earthing (also called grounding) is a vital aspect of any electrical installation. It provides a low impedance path for fault current, ensuring safety for personnel and protection of equipment. A properly designed earthing system is essential for both functional performance and compliance with international standards.

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2. Applicable Standards and Clauses

Standard	Reference Clause	Key Requirement
IEC 60364-5-54	Clause 542, 543	Design rules for earthing arrangements and protective conductors
IEC 60947-2	Annex A	Earthing requirement for protective devices
IEEE 80	Sections 7–14	Grounding design for substations
BS 7430	Full standard	Earthing system design, testing, and installation practices
Saudi Building Code (SBC 401 – Electrical)	Clause 401.10.1 to 401.10.9	National earthing and bonding requirements
NEC (NFPA 70)	Article 250	Grounding and bonding requirements in buildings

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3. Objectives of Earthing

1. Safety of human life from electric shock
2. Protection of equipment and appliances
3. Providing a reference potential for the system
4. Ensuring fast clearance of faults by enabling effective operation of protective devices
5. Lightning and surge protection

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4. Earthing System Components

Component	Function
Earth Electrode (Rod/Plate/Mat)	Provides physical connection to earth
Earthing Conductor	Connects equipment to earth electrode
Main Earthing Terminal/Bar	Common point of all earth conductors
Earth Busbar	Distribution bar for multiple earth connections
Soil Enhancing Material	Reduces soil resistivity (e.g., bentonite, conductive concrete)
Test Links	Allows disconnection for testing earth resistance
Bonding Conductors	Equalize potential difference across metallic parts

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5. Types of Earthing Systems (IEC 60364-1)

System Type	Definition	Application
TN System	Source neutral connected to earth; protective earth (PE) and neutral (N) conductors are separate or combined	Industrial, residential
TT System	Neutral earthed at source; exposed conductive parts connected to a local earth electrode	Rural areas
IT System	Neutral isolated or connected via impedance; exposed parts earthed	Hospitals, sensitive environments

TN System Subtypes:

• TN-S: Separate PE and N from the source
• TN-C: Combined PEN (protective earth and neutral)
• TN-C-S: Combined up to a point, then separate

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6. Design Criteria and Calculations (per IEEE 80 and IEC 60364-5-54)

6.1 Earth Electrode Resistance

• General Target: ≤ 1 Ω (critical systems), ≤ 5 Ω (standard installations)
• Calculation (for rod electrode): R=ρ2πL⋅(ln⁡(4Ld)−1)R = \frac{ρ}{2πL} \cdot \left( \ln\left(\frac{4L}{d}\right) – 1 \right)R=2πLρ​⋅(ln(d4L​)−1) Where:
  • RRR = Resistance in ohms
  • ρρρ = Soil resistivity (Ω·m)
  • LLL = Length of rod (m)
  • ddd = Diameter of rod (m)

6.2 Touch and Step Voltage

• IEEE 80 provides equations: Vstep=ρ⋅If2πDV_{step} = \frac{ρ \cdot I_f}{2πD}Vstep​=2πDρ⋅If​​ Vtouch=ρ⋅If2πSV_{touch} = \frac{ρ \cdot I_f}{2πS}Vtouch​=2πSρ⋅If​​
  • IfI_fIf​: Fault current
  • DDD, SSS: Distance from electrode

6.3 Equipotential Bonding

• All metallic enclosures and building structural steel must be bonded to the main earth bar.

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7. Difference Between Types of Earthing

Aspect	TN-S	TN-C	TT	IT
PE/N Separation	Separate	Combined	Separate	Separate
Fault Clearance	Fast	Fast	Depends on RCD	Slow/Alert-based
Earth Fault Current Path	Low impedance	Low impedance	Through soil	Limited current
Application	General	Cost-efficient	Remote/rural	Critical systems
Protection Device	MCB/ELCB	MCB	RCD	Isolators/alarms

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8. Saudi Standards Requirements (SBC, SEC)

• Main Earth Electrode Resistance: ≤ 1 Ω (substations), ≤ 5 Ω (buildings)
• Use of Copper Tape/Bar: Minimum 25×3 mm copper bar for equipment earthing
• Testing: Pre-commissioning earth resistance test per SBC Clause 401.10.6
• Connection Method: Exothermic welding preferred (Kingsmill or Cadweld)

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9. Testing and Maintenance

Testing Methods:

• Fall-of-potential (3-point method)
• Clamp-on method (for loop resistance)
• Soil Resistivity Test: 4-point Wenner Method (for new sites)

Maintenance Frequency:

• Visual inspection every 6 months
• Earth resistance test annually

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10. Typical Applications and Recommendations

Installation	Recommended Earthing
Data Center	TN-S with separate clean earth
Residential	TN-C-S or TT (if RCD used)
Hospital	IT System (for medical IT circuits)
Industrial Plant	TN-S with equipotential bonding
Substation	IEEE 80-compliant grid earthing

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11. Sample SLD of Earthing System

A diagram showing TN-S system with incoming supply, transformer neutral earthing, main earth bar, bonding to metallic parts, and earth electrode system.

(Will be included in the final PDF/PowerPoint version with technical drawing.)

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12. Conclusion

The earthing system is the backbone of electrical safety and system stability. A properly engineered earthing design not only ensures compliance but also protects lives, assets, and continuity of operations. It must be tailored to the site soil condition, fault levels, application type, and relevant local/international codes.

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